The present invention relates generally to the field of substrate processing equipment. More particularly, the present invention relates to a method and system for determining a height of an object on a surface. Merely by way of example, the method and system of the present invention have been applied to accurately determining z-height of an object with a rounded top, such as the proximity pin on a chuck for supporting a substrate in a processing tool. But it would be recognized that the invention has a much broader range of applicability.
Substrate support structures or chucks are widely used to support substrates within semiconductor processing systems. These chucks are used to retain semiconductor wafers or other work-pieces in a stationary position during processing. Two examples of particular types of chucks used in semiconductor processing systems include electrostatic chucks (e-chucks) and vacuum chucks.
One potential problem with such chucks is that if a substrate is loaded directly onto the upper surface of the chuck during substrate processing, the chuck surface can abrade the material present on the backside of the substrate, resulting in the introduction of particulate contaminants to the process environment. The particulate contaminants can adhere to the backside of another substrate and be carried to other process environment or cause defects in the circuitry fabricated upon the substrate. As the semiconductor device geometry has become smaller with each generation of ICs, these particulate contaminants can cause a loss in yield as well as degradation of device characteristics and reliability.
One method of reducing the number of particles generated on the backside of the substrate is to reduce the contact area between the substrate and the surface of the chuck. This can be accomplished by, for example, using an array of proximity pins or support members that space the substrate at a predetermined distance from the surface of the chuck.
Proximity pins can be installed by various methods. One known method, for example, is to form a plurality of recessed regions in the surface of the plate assembly and provide a plurality of support members with rounded shape having a diameter larger than the width of the recessed regions. Then the support members are pressed into the recessed regions to be placed into position.
An array of proximity pins manufactured in the manner described above will generally need to be characterized to ensure that each proximity pin has a height within a specification for the proximity pins. Conventional characterization processes use height measurement gauges to measure the height of protrusions on a surface. However, these height measurement gauges are not generally able to measure objects with rounded top surfaces. Additionally, height measurement gauges do not provide the resolution appropriate for some proximity pin applications. Therefore, there is a need in the art for improved techniques for measuring a height of an object on a surface.